I am in the process of wrapping the forced air heating ducts in my crawl
a material that looks like bubblewrap with foil on both sides. Does
anyone have any
idea of how much savings this will be on my gas bill? The insullation
is rated at R6, but I cannot relate this to actual savings in energy.
It's very difficult to even try to estimate without having any knowledge
of your installation/climate.
That said, chances are that it will be noticable savings if you
compare equivalent periods.
In an externally vented/drafty crawlspace, you could be losing a _lot_ of
heat from the bare ducts.
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
Ducts should be sealed with mastic first, fiberglass is better than
bubble crap, higher R and much cheaper. Best way is slide on duct
insulation. Bubble wrap I would not waste my time with and dought if it
is R 6 more likely its R 1 or less per inch
... 70 ft^2 of R1 duct might lose (130-50)70ft^2/R1 = 5.6K Btu/h to a 50 F
Wrapping the duct would save 70ft^2/R6x50F+50%RH = 633% of the gas bill? :-)
Wrapping the duct would reduce the heat loss to (130-50)70ft^2/R7 = 800 Btu/h.
Then again, with an airtight crawlspace above a vapor barrier, a lot of this
heat could end up in the house. Maybe it's better to insulate the crawlspace.
Everyone Assumes its R6, did anyone read packing lit with that stuff,
the ratings are not certified and state " Like R 6' its a BS rating
just like " Insulating ceramic paint". Its a radiant barrier, foilfaced
duct R 7 fiberglass is R 7 certified, plus radiant barrier. The price vs
effectivness of bubble wrap to fiberglass make bubble wrap a joke. after
all its just bubble wrap.
Before insulating your ducts that run thru the crawl space you will want to
seal them first -- duct mastic is considered best though I've used the foil
tape to seal all the seams. I've used foil tape that has held up very well
over ten years now. Don't use regular duct tape -- it doesn't last. Seal
the seams of the heating ducts as well as the return air ducts.
I've used the fiberglass duct insulation by Manville that I picked up at
After sealing my ducts in my crawl space and then insulating all the heating
and air return ducts I noticed a big improvement in the air flow and the
heat of the air from the registers as far as how much there are a lot of
SWAG methods that others have talked about but I do know I'm saving now for
the life of the house and since I did the work myself my only costs were
materials and time.
Sorry for not being more explicit in describing my situation. The ducts are
bare metal. I have
cut sections of the insulation and wrapped them around the cylindrical duct
pipes, sealing each
section with aluminum tape. The insulation is called Reflectix. They claim to
block up to 97%
of radiant heat. They indicate different R values for various applications, but
R-6 for bare ducts.
I know from checking that when there is hot air flowing through the ducts, the
portions are very warm to the touch, while the covered sections are barely warm
to the touch.
There is no air gap between the insulation and the pipes, but the inner 'bubble
provide some sort of trapped air barrier. I have done about 30% of the job and
decide to finish it, or not. We had very cold temperatures last few weeks in
the Chicago area,
but now the temperatures are moderating. My gas bill for December was almost
double of what
it was last year for the same number of consumed therms. This insulation sells
for about $16 for
a 16" by 25' roll, and so far I have used 2 rolls. I have not blocked the vents
in my crawl because
I want some air circulation in their to prevent mold, etc. The ceiling of the
crawl is uninsulated, so
some of the heat makes it's way through the floor to the first floor living
Reflextic, yes Ive seen that crap, as you read it says " like R6" just
like insulating paint says its "like R" whatever. The key work is "Like"
it is not a certified rating, don`t you even wonder why Reflextic has
different " like" ratings for different applications. Get a Cerfified
insulation, one that is industry accepted and known, Fiberglass. And
best is something designed for your job.
Yes, I'm sure. The bubbles hold the air inside the air space.
Install one piece correctly and the other in the haphazard way you
mentioned. Get a surface reading thermometer from Radio Shack(no, I don't
have a link) and 'shoot' the insulation. I'll bet you see a warmer surface
on the haphazard Reflectix.
I have checked further with the web site of Reflectix, which I should have done
first place. They claim their insulation gives about a 4.2 R value if applied
with no air
gap, as opposed to the R-6 value with a single air gap. This value goes up to
higher value of about R-15 if a second layer with another air gap is applied.
I somewhat fault the company for showing nice pictures of the various ways this
can be used, but nothing about how to install it over ducting to get the best
There are some instructions for crawl spaces, but nothing specific to ducts.
All they had to do was point people to their web site where everything is
explained quite clearly. Anyone can check the site yourselves at
another problem with buying at Builder stores. The prices are cheaper, but you
find anyone knowledgable about what they are selling. Hardware stores do much
better, in this respect.
With Reflectix, you only get the full R-value if you place spacers
under the wrap - read the directions carefully. The spacers are to
provide a layer of trapped air between the wrap and the ducts. You are
probably achiving significantly less than R-6.5 if you didn't do this,
but another option is to wrap the ducts twice around with the wrap.
In the real world, I can tell you that in a similar situation, crawl
with vents, uninsulated floor, my coldest room increased in temperature
approx 2-3 degrees, which is significant but not mind blowing. In our
case, it solved a sticky problem of two rooms which had had a ceiling
vaulted without a proper increase in the heating mechanics.
I do however question the wrapping of the return ducts. In that case,
the temperature differential between the duct air and the surround air
is quite a bit less than the supply duct air and the crawl air, and
therefore the heat loss is less, and less can be accomplished by
wraping. Cetainly the payback is much longer.
I would also partially block the air vents in the winter. Conditions
are so dry then from heating (in the crawl) that there should not be a
problem, and you will reduce the effect of cold air blowing up under
your floors. Only in the attic would I NOT block the vents, as your
moist heated air rises to that level.
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